sem_getvalue(3) — Linux manual page

sem_getvalue(3)          Library Functions Manual         sem_getvalue(3)

NAME         top

       sem_getvalue - get the value of a semaphore

LIBRARY         top

       POSIX threads library (libpthread, -lpthread)

SYNOPSIS         top

       #include <semaphore.h>

       int sem_getvalue(sem_t *restrict sem, int *restrict sval);

DESCRIPTION         top

       sem_getvalue() places the current value of the semaphore pointed
       to sem into the integer pointed to by sval.

       If one or more processes or threads are blocked waiting to lock
       the semaphore with sem_wait(3), POSIX.1 permits two possibilities
       for the value returned in sval: either 0 is returned; or a
       negative number whose absolute value is the count of the number of
       processes and threads currently blocked in sem_wait(3).  Linux
       adopts the former behavior.

RETURN VALUE         top

       sem_getvalue() returns 0 on success; on error, -1 is returned and
       errno is set to indicate the error.

ERRORS         top

       EINVAL sem is not a valid semaphore.  (The glibc implementation
              currently does not check whether sem is valid.)

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       attributes(7).
       ┌──────────────────────────────────────┬───────────────┬─────────┐
       │ Interface                            │ Attribute     │ Value   │
       ├──────────────────────────────────────┼───────────────┼─────────┤
       │ sem_getvalue()                       │ Thread safety │ MT-Safe │
       └──────────────────────────────────────┴───────────────┴─────────┘

STANDARDS         top

       POSIX.1-2008.

HISTORY         top

       POSIX.1-2001.

NOTES         top

       The value of the semaphore may already have changed by the time
       sem_getvalue() returns.

SEE ALSO         top

       sem_post(3), sem_wait(3), sem_overview(7)

COLOPHON         top

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Linux man-pages 6.15            2025-05-17                sem_getvalue(3)

Pages that refer to this page: sem_close(3),  sem_open(3),  sem_post(3),  sem_unlink(3),  sem_wait(3),  sem_overview(7)

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